1. Field of the Invention
The invention relates to a shaft coupling structure for coupling two rotating shafts coaxially opposed to each other to transmit rotational power from one of the rotating shafts to the other.
2. Description of the Related Art
A rotating shaft for power transmission sometimes cannot be made long because of material measurements, overhauls, and the like. In such cases, shaft division is required, and a shaft coupling is widely used as a machine element for coupling the two shafts divided.
FIG. 9 shows a shaft coupling structure 1 in wide use heretofore. In this shaft coupling structure 1, a first shaft 2 and a second shaft 4 for rotational power transmission are coaxially opposed to each other. The rotational power transmission between the first shaft 2 and the second shaft 4 is effected by a column-like member 8 having a shaft insertion hole 6 formed inside, to which the first shaft 2 and the second shaft 4 are inserted at the vicinities of their shaft ends.
To be more specific, the shaft insertion hole 6 is formed through the interior of the column-like member 8, and hence the column-like member 8 actually has the shape of a cylinder. This shaft insertion hole 6 has a key slot 10 formed therein. Similarly, the first shaft 2 and the second shaft 4 each are provided with a key slot 12. Accordingly, the first and second shafts 2 and 4 are individually engaged with the column-like member 8 in the direction of rotation via driving keys 14.
Here, safety covers 16 of short cylindrical shape are mounted on both sides of the column-like member 8 so that the heads of the driving keys 14 are prevented from exposure to exterior.
In this shaft coupling structure 1, the first shaft 2 and the second shaft 4 are coupled to each other in the direction of rotation via the column-like member 8. Therefore,for example, rotational power input to the first shaft 2 is transmitted through the driving keys 14 and the column-like member 8 to the second shaft 4 with the same rotational speed.
While this shaft coupling structure 1 has been described with the case where the shaft insertion hole 6 is formed through the interior of the column-like member 8, two shaft insertion holes may be independently formed in both ends of a column-like member 8 so as not to pass through.
Now, referring to FIG. 10, description will be given of another shaft coupling structure 20 in wide use here to fore. This shaft coupling structure 20 is of flange type. Here, a first shaft 2 and a second shaft 4 are coaxially opposed to each other. The rotational power transmission between the first shaft 2 and the second shaft 4 is effected by a first column-like member 22 having a shaft insertion hole 23 formed inside, to which the first shaft 2 is inserted at the vicinity of its shaft end, and a second column-like member 24 having a shaft insertion hole 25 formed inside, to which the second shaft 4 is inserted at the vicinity of its shaft end.
Specifically, the first and second column-like members 22 and 24 have a first flange portion 22A and a second flange portion 24A, both spreading radially outward, formed integrally on their opposing sides (the shaft-end sides of the first and second shafts 2 and 4),respectively. Each of the flange portions 22A and 24A has a plurality of bolt holes 26 formed there through along the direction of the center axis L, at regular intervals along the circumferential direction.
The first shaft 2 and the shaft insertion hole 23 in the first column-like member 22 are provided with key slots 10 and 12, respectively, so that they are engaged with each other in the direction of rotation via a parallel key 28. The second shaft 4 and the second column-like member 24 are in the same relationship.
The first flange portion 22A and the second flange portion 24A are coupled to each other by bolts 30 inserted through the bolt holes 26 and nuts 32 threadedly engaged with the bolts 30, so that the flange portions 22A and 24A make integral rotation.
Therefore, for example, rotational power input to the first shaft 2 is transmitted through the parallel key 28, the first column-like member 22, the bolts 30 and nuts 32, the second flange portion 24A, and the parallel key 28 in this order, to the second shaft 4 with the same rotational speed.
Here, though separate in form, the first column-like member 22 and the second column-like member 24 are substantially in an integral structure due to the bolts 30 and the nuts 32, much the same as the shaft coupling structure 1 shown in FIG. 9. Note that this shaft coupling structure 20 of flange type is particularly convenient when the first shaft 2 and the second shaft 4 have different shaft diameters, since the first column-like member 22 and the second column-like member 24 can be made of different members.
Next, description will be given of an example where the shaft coupling structure 1 shown in FIG. 9 is applied to a driving apparatus for a rotary machine.
A rotary-machine driving apparatus 34 shown in FIG. 11 comprises a motor 36 having a motor shaft 36A, a speed reducer 42 having an input shaft 38 and an output shaft 40 in parallel, and a joint casing 44 for combining the motor 36 and the speed reducer 42 integrally. Here, the same shaft coupling structure 1 as that shown in FIG. 9 is used to couple the motor shaft 36A and the input shaft 38 to each other.
That is, turning to the relation between FIGS. 9 and 11, the first shaft 2 corresponds to the motor shaft 36A, and the second shaft 4 to the input shaft 38. Rotational power from the motor shaft 36A is thus transmitted through this shaft coupling structure 1 to the input shaft 38 with the same rotational speed.
The role of the joint casing 44 is to couple the motor 36 and the speed reducer 42 integrally so as not to make relative rotations. The joint casing 44 typically uses a circular cylindrical or square cylindrical member. In this connection, while this driving apparatus 34 has a structure of mounting the motor 36 directly onto the speed reducer 42 via the joint casing 44, the motor 36 and the speed reducer 42 may be separately fixed to an independent motor base, speed-reducer base, and the like. In such a case, a safety cover and the like may be installed to prevent the shaft coupling structure 1 from exposure.
Note that a shaft coupling structure sometimes functions to avoid a breakage of apparatuses to be connected. Suppose, for example, that the rotation of the speed reducer 42 in FIG. 11 is suddenly locked in an accident. Even so, the column-like member 8, the driving keys 14, or other components in the shaft coupling structure 1 can break down first to avoid an overload on the motor 36 and the like.
Nevertheless, as is evident from FIG. 11, there is plenty of room around the shaft coupling structure 1 (including the internal space of the joint casing 44 and the joint casing 44 itself) which has not been put into any use at all.
The reason for this is that the motor 36, the speed reducer 42, and other apparatuses having rotating shafts (input shaft 38, motor shaft 36A) has certain dimensions while the shaft coupling structure 1 for coupling the rotating shafts has highly compact configuration. That is, the space between the apparatuses arranged on both sides of the shaft coupling structure 1 actually has had no particular uses beneficial, other than to arrange a simple joint casing 44 or to install a safety cover over the shaft coupling structure 1 at best.
On the contrary, if the space described above is utilized, such utilization as involves an axial extension of the shaft coupling structure 1 and/or production of greater noise would be nothing more than confusion even in terms of shaft coupling functions.
The present invention has been achieved in view of the foregoing problems. It is thus an object of the present invention to provide a shaft coupling structure which maintains and exerts the functions inherent to a shaft coupling structure as well as utilizes the empty space around the to-be-coupled two shafts for an additional speed change function.
The foregoing object of the present invention has been achieved by the provision of a shaft coupling structure with speed change function comprising a first shaft and a second shaft coaxially opposed to each other, and a member for coupling the first shaft and the second shaft to each other, rotational power transmission between the first shaft and the second shaft being effected by the member. Here, the member is divided into first-shaft side and second-shaft side so as to form a first transmission member and a second transmission member for making integral rotation with the first and second shafts, respectively. A plurality of planetary rollers and a ring roller are arranged around the first transmission member. The plurality of planetary rollers make rolling contact with the outer periphery of the first transmission member and with the inner periphery of the ring roller, and the ring roller is engaged with a non-rotational member for rotational restraint. The second transmission member supports the plurality of planetary rollers rotatably so that the second transmission member makes rotation integral with the revolution of the plurality of planetary rollers around the first transmission member.
More specifically, as shown in FIGS. 1 and 2, a column-like member (as shown in FIGS. 9 and 10) is divided into a first-shaft-2 side and a second-shaft-4 side to form a first transmission member A and a second transmission member B for making integral rotations with the shafts (the first shaft 2 and the second shaft 4), respectively. A plurality of planetary rollers C are arranged around the first transmission member A so as to make rolling contact with the outer periphery A1 of the first transmission member A. Besides, a ring roller D with the inner periphery D1 of which the plurality of planetary rollers C make rolling contact is arranged so as to be restrained on rotation by an external non-rotational member F.
Moreover, each of the plurality of planetary rollers C is rotatably supported by a second transmission member B. As a result, the second transmission member B can make rotation integral with the revolution of the planetary rollers C around the first transmission member A.
In such configuration, the first transmission member A and the second transmission member B can be regarded as a sun roller and a carrier, respectively, which means that this shaft coupling structure also serves as a simple planetary roller mechanism using frictional rollers. Accordingly, given that the first transmission member A makes the input element of rotational power, the shaft coupling structure functions as a reduction mechanism with the second transmission member B as the output element. When the second transmission member B makes the input element of rotational power, the shaft coupling structure functions as a step-up mechanism with the first transmission member A as the output element.
In the meantime, this shaft coupling structure provided with speed change function loses none of the inherent shaft coupling functions despite the configuration as described above.
The reasons for this will be detailed below.
First, both the first transmission member A and the second transmission member B have a shaft insertion hole formed therein, and the first transmission member A and the second transmission member B are arranged on the same axis. This preserves the shaft coupling""s essential function of xe2x80x9ccoupling the coaxially-opposed first and second shafts 2 and 4 to transmit rotational power.xe2x80x9d
Second, the rotational power is transmitted through the contact surfaces of the frictional rollers, i.e., of the planetary rollers C and the ring roller D. Therefore, the transmission produces no particularly high noise, preserving the property of xe2x80x9cquietnessxe2x80x9d required of a shaft coupling.
Third, this shaft coupling structure with speed change function is configured so that the contact surfaces of the rollers make a slip when subjected to rotational torque above a predetermined value. Therefore, even if an overload suddenly occurs on one of the rotating shafts, a breakage of the apparatus connected to the other rotating shaft can be avoided to a certain extent. In other words, this shaft coupling structure also offers the function of xe2x80x9csafetyxe2x80x9d required of a shaft coupling.
This shaft coupling structure with speed change function is somewhat greater in radial dimension due to the presence of the planetary rollers C and the ring roller D. This, however, means utilization of the space around a shaft coupling which has been wasted (not utilized) as stated before. Accordingly, the entire apparatus coupled will not be affected in size.
As is also evident from above, this shaft coupling structure with speed change function is provided with a high-ratio speed change function without losing the conventional shaft coupling functions. Therefore, when this shaft coupling structure is applied e.g. to couple a motor and speed change gears, it is possible to lower the gear ratio of the change gears to be coupled since the shaft coupling structure itself can achieve a certain change in speed. This makes the entire apparatus more compact.
The non-rotational member for restraining the rotation of the ring roller may come into engagement with and support the ring roller, and comprise a pair of flange portions spreading radially outward on the first and second transmission members, the flange portions being capable of establishing connection between a casing on the first-shaft side and a casing on the second-shaft side so that the rotation of the non-rotational member is restrained. In this case, the easy coupling between the first-shaft side and the second-shaft side can extend to the casings. In addition, the ring roller can be easily maintained in a non-rotational state.
Incidentally, FIG. 1 has shown, in functional terms, the ring roller D being engaged with an external non-rotational member for rotational restraint as fitted and fixed directly to the casing for accommodating this shaft structure. The means for the rotational restraint, however, is not limited thereto. For example, the ring roller D may be restrained on rotation by bolting, or by providing a projection on the ring roller D for engagement with the external non-rotational member. It is essential only that the rotation of the ring roller D be restrained in some way.
Moreover, the first and second transmission members A and B are not limited to certain specific configurations, and need not always have a column shape.
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.